Dodonaea viscosa 'Atropurpurea' or Tecomaria capensis are two larger growing shrubs that would take that exposure with water, and get large enough to give some wall shade. Oleander would also work. All of these would need regular trimming to keep them in bounds with just 4 feet of planter area. If shade on the wall weren't the issue, I would rather plant something like Hesperaloe for the blooms all summer, possibly in combination with Agave parryi or similar. Tecoma stans would also work for you, or you could plant a vine such as Macfadyena unguis-cati on a trellis, or Merremia.

Bismarckia nobilis is a cool looking palm, but can get frost damage in Phoenix, and they need an awful lot of summer water to grow well in the desert. Brahea armata might be a more water wise choice of palm, with similar silver coloration.

Thanks for the info. I've quickly found photos of some of the plants you suggested, and they look promising. I'll more reading later.

A bit more research indicates that the plants that I saw labeled as Madagascar Palms were not Bismarckia nobilis, but rather Pachypodium lamerei. I've got a link below for anyone who is interested -- they've very strange.

Here is a link that might be useful: Madagascar Palm

That western exposure in Phoenix is tough and really limits your choices. Bahia has some good suggestions although here in Las Vegas I've not found the purple hopseed bush(dodonaea) to handle the desert heat well. If you need the height with a width of no more than four feet it seems like you would have to go for a vine. Besides the ones suggested what about bougainvillea? Ours loves the sun and heat and will easily cover your space with quite a bounty of flowers.

If you can have something that spreads out a bit more on top the Caesalpinias are very showy and tropical looking. Myrtus Communis Boetica takes a lot of sun and has a more evergreen traditional look with a twist but it is slow growing. The cordias are wonderful (Parvifolia and boissieri) and have fresh looking white flowers all through the summer but they might not want to be kept very narrow.

Texas mountain laurel (sophora secundiflora) is another nice evergreen heatloving tree/shrub that blooms in the spring. It doesn't look like a desert plant but does well here although it is not a quick grower.

Good idea to wait until fall to start your new project, Maria

Unfortunately, anything requiring a trellis is going to be out of the question due to HOA rules. However, after doing some more reading on the suggestions in this thread, I've noticed that several houses in the neighborhood have healthy-looking oleanders planted against south- and west-facing walls. While ideally I'd like something a bit unusual, I'd rather pick something that I know will do well and just confine my creativity to my garden.

Thanks again to both of you - if anyone else has any suggestions, I'd love to hear them.